This invention relates to an improved seat hinge mechanism and more particularly to one adapted for use with a motor vehicle occupant seat which permits the seat back to be normally folded forward to permit access to a rear compartment area but which locks to prevent folding when vehicle predetermined forward deceleration loads are sensed.
Most present passenger motor vehicles have a rear seat occupant or luggage compartment area. In two-door style vehicles, a means for accessing such areas is necessary. Ordinarily, such access is provided through the use of a front seat having a seat back which is foldable in a forward direction relative to the seat bottom. Present Federal Motor Vehicle Safety Standards applicable in the United States require a locking mechanism which restrains forward rotation of a folding type seat back in the event of a frontal collision. In the past, folding seats were provided with a manually actuated seat back latch. As a means of improving user convenience, many modern motor vehicle models incorporate an inertia sensitive element within the seat hinge mechanism which enables the seat back to be folded forward without significant resistance when the vehicle is at rest or during ordinary operating conditions. In the event, however, that the vehicle is subjected to a forward deceleration load, such as experienced during hard braking or frontal impact, the seat hinge mechanism is latched to restrict forward rotation of the seat back. Many presently available seat hinge mechanisms incorporating inertia sensitive locking devices further provide a mechanism for positioning the inertia sensitive element in an engaged position when the seat back is folded to its rearmost position. For such mechanisms, the inertia sensitive actuator is freed to move between engaged and released positions once the seat back is folded forwardly several degrees. In the event that the vehicle is subjected to deceleration loads above a predetermined level, the inertia sensitive actuator remains in an engaged position, thus preventing forward seat back rotation. Such seat hinge designs which position the inertia sensitive element in an engaged position when the seat is folded back have the advantage that they continually cause the element to be moved between engaged and released positions, thus reducing the likelihood that corrosion, foreign matter, etc. would interfere with free movement of the actuator.
Although seat hinge mechanisms having the above-discussed features are presently known, there is a continuing need to provide improvements for such mechanisms. Designers of mass-produced components such as those used in modern motor vehicles are constantly striving to reduce their complexity and cost. Many present designs of seat hinge mechanisms having the above-discussed features present an edge surface which protrudes toward the rear seat area when the seat back is rotated forward. This edge surface can be objectionable in that rear seat occupants could contact it while entering or egressing the rear seat area. Accordingly, it is desirable to provide a seat hinge which does not interfere with free access to the rear compartment area. Seat reclining mechanisms having inertia sensitive actuators are required to have an emergency release which overcomes the inertia sensitive actuator to enable a rear seat occupant to release the seat back in an emergency condition to permit escape from the vehicle. Emergency releases are typically in the form of a manually operable handle which acts on the inertia sensitive element to forcibly move it to a freeing position. Since the emergency release actuator must be accessible to the rear seat occupant, it is necessary to provide a lever which protrudes from the seat back and therefore the seat trim must accommodate such protrusion. In order to simplify trimming of the seat back, it is desirable to locate the emergency release actuator at a position near the pivot of the seat back and seat bottom.
The hinge mechanism in accordance with this invention achieves the above-mentioned desirable characteristics. The hinge structure incorporates a component carried by the lower hinge structure which forms a stop surface and an actuator biasing surface. An inertia sensitive pawl having its center of gravity located above and behind its center of rotation is provided which interacts with the stop surface when the vehicle is subjected to a forward deceleration above a predetermined value, thus preventing forward seat back rotation. The actuator biasing surface engages the actuator to urge it to an engaged position when the seat is in its rearmost positon. The inertia actuator according to this invention is compact and simple in construction and operation. The configuration and placement of the inertia actuator according to this invention permits the emergency release mechanism to be positioned at a point near the junction between the upper and lower seat hinge structures, thereby simplifying trimming of the seat.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims taken in conjunction with the accompanying drawings.